P.Nigra Color Transformation Observation

[Lot 112]

I have noticed that P.Nigra is popular with Los Angeles based landscape designers,I've started noticing it in several locations(Ion Bar J.W. Marriot DTLA & in the courtyard of the mall on Sunset & Crescent Heights to name a few). The P.Nigra is contained in concrete planters & topped & jet black with the exception of the new shoots.

I've noticed that when a P.Nigra cane is topped it accelerates the color transformation. I have a few shoots which were snapped by birds perching on the them which have turned completely black,their counterparts which have reached their full height are still molted. Why does topping P.Nigra accelerate the color transformation process?

[watchnerd]

I think this is a classic example of "ad hoc ergo propter hoc", i.e. "If A happens, then B happens, then A causes B". This is a logical fallacy.

We know that blackness in P. nigra definitely relates to age (older = blacker), and some think it relates to the amount of sunlight.

It could very well be that all the P. nigra you are seeing in hotel planters and the like are very black simply because they are old. They also happened to be topped. That doesn't mean the topping causes the blackness.

As for your example with the birds, we'd need a bigger sample size than one to draw any conclusions.

[Alan_L]

I think the "birds topped a few of my new culms..." example is quite interesting, and does indicate some sort of causal relationship. I agree it needs more testing though.

How much of the culm was snapped off? 25 percent? 50 percent? I think we could convince some people on this forum to top a couple of nigra culms and see what happens.

[watchnerd]

We'd also need to separate the effects of topping from those of light changes, as topping the culm could easily change the amount of light coming in.

[foxd]

Several years ago I tried sheilding a section of Ph. nigra culm from sunlight to see if there was any difference between the shaded and unshaded area after a month. There wasn't.

There was also a posting on Gardenweb(?) where the experiment was claimed to have been done and gave a positive result. However the images showed a lot of evidence of the use of Photoshop.

My hypothesis is that the color change has something to do with the presence of moisture, perhaps affecting the absorption of some trace element (copper?).

The rate of change varies wildly from year to year, taking from a couple of months to over a year.

One of those experiments I've been meaning to try is to pin down exactly what to do to trigger the change in color.

[bamboothew]

Hmm...I have nigra in several spots so I will make a point to do some such experiments in a couple of years. I will tell you that the clone I found a a feral grove last winter seems to send up new shoots that are very spotted with black at sheath fall, regardless of the light exposure or soil composition, and I have some in both full sun and almost full shade, some in rich potting soil and some in red clay. I think this will prove to be an interesting clone. It does seem to be a very floppy clone , though.